Chloride channels are ubiquitous proteins found in invetebrates to man
. Cl- is one of the most abundant biological anions and accounts for a
measurable fraction of the electrical conductance of many biological
membranes. Physiologically this contributes to cellular processes, inc
luding pH regulation, volume regulation, generation of the resting mem
brane potential, and regulation of membrane excitability. The unitary
conductance of voltage-dependent Cl- channels is as diverse as the num
ber of different types of Cl- channels described ranging from 5-450 pS
. Cl- channels are highly anion selective passing at least ten anionic
species, including all of the halides. Cl- channels are blocked by va
rious agents, including aromatic acids, inorganic cations, and protons
. Maintaining high resting conductance and normal excitability, regula
ting cell volume, and modulating hormone action are some examples of t
he functions of Cl- channels. Despite the large amount of data accumul
ated on voltage-dependent Cl- channels, identifying subsets within thi
s class of channels with coherent biophysical features that subserve e
ach specific function is still not possible. At present, the molecular
structure for every type of functional Cl- channels has not been dete
rmined, but future identification of cloned Cl- channel structures sho
uld provide a clearer understanding of the functional properties of ba
ckground Cl- channels. (C) 1996 Wiley Liss, Inc.